1. Field of the Invention
The present invention relates to a high-frequency module and a radio communication apparatus. More particularly, the present invention relates to a high-frequency module which is suitable for a multi-band mobile radio terminal and on which there are mounted power amplifiers, switch circuits, a diplexer, directional couplers, an auto power controller and the like, and also to a radio communication apparatus having such a high-frequency module mounted thereon.
2. Description of Related Art
Recently, there is proposed a cellular phone of the multi-band type in which two or more transmission/reception systems are mounted in a single cellular phone.
Such a multi-band type cellular phone is expected as a highly convenient device because transmission/reception can be made by selecting the transmission/reception system suitable to the regional characteristics, intended purpose and the like. For example, there are now widespread dual-band cellular phones on which two systems of the GSM (Global System for Mobile Communications)/DCS (Digital Cellular System) are mounted.
FIG. 16 is a block diagram of a high-frequency circuit unit of a dual-band cellular phone of the GSM/DCS systems.
The high-frequency circuit unit has a high-frequency switch module ASM1 arranged to branch the two transmission/reception systems GSM/DCS different in pass band from each other, and to switch the transmission system TX and the reception system RX in each transmission/reception system DCS, GSM. The high-frequency switch module ASM1 comprises low-pass filters, switch circuits and a diplexer, and is further provided with the transmission system DCS TX and the reception system DCS RX of the transmission/reception system DCS, and the transmission system GSM TX and the reception system GSM RX of the transmission/reception system GSM.
The transmission systems DCS TX, GSM TX respectively have directional couplers COP100, 200, and power amplifiers AMP100, 200. Each of the power amplifiers AMP100, 200 is formed by a power high-frequency amplifying element MMIC and a matching circuit.
At the transmission time, a transmission signal amplified by the power amplifier AMP100 or AMP200, is transmitted, as a high-frequency signal, from an antenna ANT through the directional coupler COP100 or COP200 and the high-frequency switch module ASM1.
On the other hand, the reception systems DCS RX, GSM RX respectively have band-pass filters BPF300, BPF400 and low-noise amplifiers AMP300, AMP400. At the reception time, a high-frequency signal received at the antenna ANT is taken out through the high-frequency switch module ASM1, and then amplified by the RX-side low-noise amplifier AMP300 or AMP400 after an unnecessary signal in the vicinity of the reception band has been removed by the band-pass filter BPF300 or BPF400.
In a cellular phone of the dual-band type, it is required to mount circuits necessary for both transmission/reception systems. When the circuits are formed by using individually dedicated components, this disadvantageously increases the device size and costs.
It is therefore required to advantageously develop an approach for smaller and more economical devices by standardizing circuit components as much as possible.
It is further required to improve the power added efficiency of the power amplifiers which consume the greater part of the power of a cellular phone.
In a cellular phone of the multi-band type, however, the component elements of the high-frequency switch module, the power amplifiers, the matching circuits, and the directional couplers are mounted on a printed circuit board, so that a further miniaturization cannot be expected.
On the other hand, a high-frequency amplifier circuit to be mounted on a conventional high-frequency module is generally a multi-stage amplifier in which a plurality of high-frequency amplifying elements are connected in series. A voltage-supply bias line is connected to each high-frequency amplifying element, to which a direct-current voltage is supplied. Provision is made such that this voltage-supply bias line serves as a stub having a ¼ wavelength with respect to a high frequency signal. This prevents the high-frequency signal from entering into the direct-current voltage source.
Further, the electric characteristics of the multi-stage high-frequency amplifying elements are adjusted such that the output power, the harmonic component and the like satisfy the standards by an output matching circuit connected at the last stage.
As is often the case with a multi-stage amplifying circuit in which a plurality of high-frequency amplifying elements are connected in series, there is a problem with the relationship between the output power and the output control voltage in a conventional high-frequency module. That is, the waveform is distorted at the point where the operation of a high-frequency amplifying element is switched to the next stage. Accordingly, the relationship between the output power and the output control voltage does not disadvantageously linearly change as shown in FIG. 15.
Therefore, when such a conventional high-frequency module is mounted on a cellular phone at its terminal and the output power is intended to be controlled, it takes much time to obtain the desired power. In the worst case, there is a possibility that two or more output control voltage values exist for obtaining the desired power, so that the output power cannot be controlled.
To improve the above problem, it is required to change the designing of the gain and the like of the high-frequency amplifying elements at each stage of each power amplifier. Thus, much time and cost are required for obtaining the effects of the improvement in characteristics.